In the printing of pressure sensitive labels, for example, with a hand-held portable labeler of the type disclosed in U.S. Pat. No. 4,252,060 which issued to the Assignee of the present invention, it is common to apply ink to the selected printing characters on the endless printing bands or wheels with an ink roller. The ink roller may be of the type which incorporates a micro-porous ink retaining flexible sleeve mounted on a spool for rotation. A supply of ink is carried by the micro-porous sleeve so that the ink roller is capable of supplying sufficient ink to print one or more supply rolls of pressure sensitive labels.
In the printing of labels with characters or codes which are read by optical character recognition equipment, it is important for the printing to meet high quality standards. That is, the labels must be uniformly and precisely printed without a drop off or diminish in printing quality as the supply of ink is consumed from the microporous ink roller sleeve. Different forms of ink roller assemblies have been made or proposed in order to incorporate within the ink roller a larger supply of ink, for example, as disclosed in U.S. Pat. Nos. 2,663,257 and No. 3,738,269. Each of these patents disclose the use of capillary ink retaining passages or chambers within a surrounding band or sleeve of micro-porous ink retaining material.
In such an ink roller assembly, it is desirable to maximize the liquid ink storage capacity of the roller assembly while also providing for optimum flow rate control or metering of the ink from the storage reservoir or chambers to the application sleeve so that the ink applied by the sleeve remains substantially constant or uniform throughout the usable life of the roller assembly. It is also desirable to construct the ink roller assembly in a manner which prevents leakage of ink from the roller assembly in response to sudden changes in temperature or atmospheric pressure. After analyzing the ink roller assemblies disclosed in the above-mentioned patents, it is apparent that these ink roller assemblies do not provide all of the above desirable features.